In the past, a printing method has been known in which color inks are ejected on a print sheet from a plurality of ink jet heads for different colors aligned in order along a transfer path formed by a high-speed conveyor belt. Recently, with increased demand for high-speed printing, this type of printing system is equipped with a conveyor belt that runs around the path at a high speed. This type of printing system equipped with a high-speed conveyor belt transfers a print sheet (print paper) from a paper feed unit to the line type ink jet heads by the conveyor belt running around at a high speed, performs printing on the print sheet which is passing through a transfer path, and discharges the print sheet as printed from a discharge unit (refer to Patent Document 1).
Incidentally, in the case of the configuration disclosed in the above Patent Document 1, a print sheet is sometimes obliquely transferred in relation to the transfer direction of the print sheet during transferring the print sheet from the paper feed unit to the ink jet heads, as called oblique transfer. Because of this oblique transfer, the position of the print sheet may be misaligned in relation to the ink jet heads to apply an excessive tension to the print sheet resulting in wrinkles or fracture.
Because of this, in the past, it was proposed to give an extra length to the print sheet by warping the print sheet when feeding the print sheet to the transfer path from the paper feed unit, regulate the arriving direction by the elastic force of the warping and absorb or release excessive tension acting on the print sheet.
However, in the case of this mechanism to warp the print sheet as described above, the elastic force of warping may become excessive depending upon the size, thickness or material of the print sheet to displace the print sheet in relation to the conveyor belt. If printing is started in this condition, the print position is misaligned to degrade the printing quality. As a design method for avoiding the above shortcoming, it may be conceived to place no ink jet head in the area where the print sheet may be displaced. However, in this case, the distance between the paper feed unit and the ink jet head becomes too large, resulting in a bigger design. [Patent Document 1] Japanese Patent Published Application No. 2004-276486